This invention relates to a process for the production of high purity bisphenol A.
One known method of producing bisphenol A (2,2-bis(4xe2x80x2-hydroxyphenyl)propane) includes reacting acetone with excess phenol in the presence of a strong acid catalyst such as a sulfonic acid-type cation ion exchange resin. The product is generally cooled to form crystals of an adduct of bisphenol A with phenol (hereinafter referred to simply as xe2x80x9ccrystalline adductxe2x80x9d). The crystalline adduct is collected and is then subjected to a phenol removing treatment to obtain a high purity bisphenol A. The phenol removing treatment is generally performed by heating a melt of the adduct to vaporize and separate phenol using, for example, a distillation tower.
It has been found that during the phenol removing treatment, bisphenol A is thermally decomposed to form impurities such as phenol and isopropenyl phenol. The decomposition of bisphenol A proceeds not only in the phenol removing device but also in a line downstream of the phenol removing device through which bisphenol A separated is discharged for recovery. It has also been found that it is difficult to avoid the decomposition of bisphenol A in the phenol removing step by mere control of the conditions of the phenol removing step.
The present invention has been made in view of the above problem.
The present invention provides a process for the production of bisphenol A, comprising providing a melt of a crystalline adduct of bisphenol A and phenol which contains a strong acid contaminant, and heating said melt to vaporize and remove phenol from the melt, characterized in that, before said heating, said melt is contacted with a cation donating solid to neutralize the strong acid contaminant therewith.
It has been found that thermal decomposition of bisphenol A during the phenol removing treatment is ascribed to the presence of a strong acid contaminant such as sulfuric acid or sulfonic acid in the crystalline adduct. The strong acid contaminant is considered to be derived from the strong acid catalyst used for the reaction of acetone with phenol.
The amount of the strong acid contaminant in a melt of the crystalline adduct is generally 0.003 meq/liter or less, typically 0.0001-0.001 meq/liter. By contacting the melt with a cation donating solid, such a trace amount of the strong acid contaminant has been found to be effectively neutralized in a stable manner irrespective of variation of the amount of the acid contaminant. With a liquid alkaline substance, it is impossible to neutralize such trace amount of a strong acid in a stable manner.
Any cation donating solid may be used for the purpose of the present invention as long as the strong acid contaminant can be neutralized therewith or converted into a substance, such as a salt, which no longer exhibits properties of a strong acid.
Examples of cation donating solids include cation exchange resins (such as xe2x80x94COOM type where M is a cation), inorganic ion exchangers (such as silicate (e.g. zeolite or silicalite) substituted by a cation), ceramics (e.g. glass and porcelain) containing an alkali metal oxide (e.g. Na2O) and/or alkaline earth metal oxide (e.g. CaO), alkali metal compounds and alkaline earth metal compounds. The cation donating solid may be in any desired shape such as powder, granule (pellet), fiber, plate, porous plate, film, sheet or cylinder.
As the cation, there may be used alkali metal ions, such as sodium ions, potassium ions or lithium ions; alkaline earth metal ions, such as calcium ions or magnesium ions; ammonium ions; and organic ammonium ions derived from organic amines.
The contact of a melt of the crystalline adduct with the cation donating solid may be carried out in any desired method such as a packed tower method in which the melt is passed through a packed tower containing the cation donating solid, a filtration tower method in which the melt is passed through a filtration tower containing a layer of the cation donating solid, a dispersing method in which powder of the cation donating solid is dispersed in the melt, or a immersion method in which a molded body of the cation donating solid is immersed in the melt. Through the contact of the melt with the cation donating solid, the strong acid contaminant in the melt is neutralized by ion exchange reaction with the cation on surfaces of the solid.